fix: fail startup when Auth0 is not configured

[katyalmohit]

Pull Request

Description

• Missing AUTH0_DOMAIN/AUTH0_AUDIENCE used to silently fall back to DummyBackend,
  authenticating everyone as dummy|123456 and leaving all v0 routes open. The app now refuses to start when ENVIRONMENT=production.
• Other environments keep the existing dummy-auth fallback and warning.

Fixes #https://github.com/openclimatefix/client-private/issues/560

How Has This Been Tested?

Ran locally with ROUTERS=uk_national SOURCE=dummydb and the Auth0 vars unset

Checklist:

• My code follows OCF's coding style guidelines
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked my code and corrected any misspellings